You would need something like this. http://www.ebay.com/itm/Farenheit-LP-2CSC-Chrome-License-Plate-Backup-Camera-w-Parking-Sensors-/360896138642?pt=LH_DefaultDomain_0&hash=item5407160d92&vxp=mtr
This is exactly what I have connected to my unit.
It is a camera that has the parking sensors built into it. It comes with a seperate module with a speaker that notifies you of your distance and beeps when you are too close.

For all of you who are having problems with the Z140BT, it seems as though the problem is with the CARDINFO.cif not being compatible with the head unit. I'll keep you posted if I make any progress. But since I do not have a Z140BT, it might take a while.